Eosinophils of the horse: Part I: Development,distribution, structure and biochemical mediators

Eosinophils are becoming the target of increasing research interest as recent studies suggest that their role in immune homoeostasis and the immune response to disease is far more complex than previously understood. Historically, the horse eosinophil has been used to study basic eosinophil biology because of the considerable volume of blood required to obtain enough viable cells for reliable, repeatable experiments. This resulted in a large but disseminated body of literature pertaining to the structure and function of the horse eosinophil. More recently, equine clinicians have produced case reports and clinical studies in an effort to define the role of the eosinophil in diseases of the horse. A thorough review of the equine eosinophil incorporating both bench research and clinical reports does not exist. The objective of this two-part review is to fill this need by integrating the basic science and clinical research into a comprehensive body of work on what is known specifically about the horse eosinophil, and its role in equine health and disease. Part I summarises the development and tissue distribution of eosinophils in the normal horse, and presents what is known about the cell structure, migration and biochemical mediators of the horse eosinophil. Part II reviews the role of the eosinophil in diseases of the horse, and concludes with a summary of knowledge gaps and open research questions to benefit both those who wish to use the equine eosinophil as a model for basic science research, and those whose primary interest lies with diseases of horse.     

Chronic idiopathic inflammatory bowel diseases of the horse

A review of reported cases of inflammatory bowel diseases (IBDs) of horses for which no etiology was identified included cases of granulomatous enteritis (GE), multisystemic eosinophilic epitheliotropic disease (MEED), lymphocytic-plasmacytic enterocolitis (LPE), and idiopathic eosinophilic enterocolitis (EC). The terms EC and MEED were both used to describe a disease in horses characterized by infiltration of intestine and extraintestinal tissues with eosinophils. We use EC to describe IBD characterized by only intestinal infiltration by eosinophils. Horses with GE, MEED, or LPE are usually examined because of weight loss and depression, but horses with EC are usually examined because of signs of abdominal pain. Typically, horses with IBD have low concentrations of serumal proteins, especially albumin, and fail to adequately absorb glucose or xylose. Antemortem diagnosis of IBD can only be made by histologic examination of affected intestine. In some cases, antemortem diagnosis is made from histologic examination of rectal mucosa obtained by biopsy. Suspected causes of IBD in the horse include abnormal immune response to bacterial, viral, parasitic, or dietary antigens. Most horses with IBD do not survive, but horses with EC are more likely than those with LPE, MEED, or GE to respond to treatment. Successful treatments of horses with IBD include resection of grossly affected intestine and administration of corticosteroids.     

Role of the chemokine eotaxin in the pathogenesis of equine sweet itch

The chemokine eotaxin is involved in the recruitment of eosinophils and T helper 2 lymphocytes in human allergic diseases, and drugs that block its activity, including eotaxin receptor (CCR3) antagonists, are being developed. The authors have recently cloned the horse ortholog of eotaxin and shown that it can induce equine eosinophil migration and activation in vitro. Moreover, eotaxin mRNA expression was upregulated in cultured horse dermal fibroblasts exposed to equine interleukin-4, suggesting a possible source of this eosinophil chemoattractant in equine skin. The results of this study show that eotaxin and monocyte chemoattractant protein (MCP) 1, but not MCP-2 or MCP-4, mRNA expression is upregulated in skin biopsies of sweet itch lesions when eosinophils are present, when compared with clinically normal skin from the same ponies.     

The effects of Strongylus vulgaris parasitism on eosinophil distribution and accumulation in equine large intestinal mucosa

REASONS FOR PERFORMING STUDY: Eosinophilic granulocytes have been associated with parasite or immune-mediated diseases, but their functions in other disease processes remain unclear. Cause and timing of eosinophil migration into the equine gastrointestinal mucosa are also unknown. OBJECTIVE: To determine the effects of intestinal parasitism on eosinophils in equine large intestinal mucosa. METHODS: Large intestinal mucosal samples were collected from horses and ponies (n = 16) from the general veterinary hospital population, ponies (n = 3) raised in a parasite-free environment, ponies experimentally infected with 500 infective Strongylus vulgaris larvae and treated with a proprietary anthelmintic drug (n = 14), and a similar group of ponies (n = 7) that received no anthelmintic treatment. Total eosinophil counts and eosinophil distribution in the mucosa were determined by histological examination. A mixed model analysis was performed and appropriate Bonferroni adjusted P values used for each family of comparisons. P<0.05 was considered significant. RESULTS: There was no difference in large intestinal mucosal eosinophil counts and eosinophil distribution between ponies infected with S. vulgaris and those raised in a parasite-free environment. Experimental infection with S. vulgaris, with or without subsequent anthelmintic treatment, did not change eosinophil counts, and counts were similar to those for horses from the general population. CONCLUSIONS: Migration of eosinophils to the equine large intestinal mucosa appears to be independent of exposure to parasites. Large intestinal mucosal eosinophils may have more functions in addition to their role in defence against parasites.     

Determination of the activity of pyrantel tartrate against Sarcocystis neurona in gamma-interferon gene knockout mice

Equine protozoal myeloencephalitis (EPM) is the most important protozoal disease of horses in the United States. Some horse owners and equine clinicians believe that horses which are on daily pyrantel tartrate at 2.64mg/kg for helminth prophylaxis are less likely to develop EPM. The present study examined the efficacy of pyrantel tartrate in preventing clinical disease in gamma-interferon gene knockout (BALB/c-Ifng(tm1ts)) mice. No activity was seen against sporocyst-induced Sarcocystis neurona infections in mice treated prophylacticly with 4-5mg pyrantel tartrate per mouse per day in the drinking water.     

Equine multisystemic eosinophilic epitheliotropic disease: A case report and review of literature

CASE HISTORY: A 2-year-old Standardbred gelding presented with a history of fever over 1 week, anorexia and skin lesions on all four legs. The lesions were associated with severe pruritus and oedema, and there was no response to therapy.

CLINICAL FINDINGS: The horse was in poor body condition, was lethargic and severely pruritic. Skin lesions consisted of diffuse alopecia and crusting of the distal extremities. Initially it was slightly febrile, but subsequently its temperature increased up to 40°C. Ten days after admission it developed profuse watery diarrhoea and the skin lesions progressed. Skin biopsies revealed superficial and deep perivascular dermatitis with lymphoplasmacytic and eosinophilic predominance. Based on the poor prognosis the horse was subject to euthanasia.

PATHOLOGICAL FINDINGS: The most notable lesions included ulcerative gastritis, typhlitis and colitis with prominent oedema of the intestines, marked subcutaneous oedema and severe thickening of the large bile ducts. Histopathology showed marked eosinophilic and lymphoplasmacytic infiltration of various tissues including the skin, gastrointestinal tract, mesenteric lymph nodes, large bile ducts, pancreatic duct and kidney. Immunohistochemistry revealed a clear predominance of CD3-positive cells in the lymphocytic infiltrations.

DIAGNOSIS: Based on the clinical findings and histopathology a diagnosis of multisystemic eosinophilic epitheliotropic disease (MEED) was made.

CLINICAL RELEVANCE: Multisystemic eosinophilic epitheliotropic disease is rare in horses, and usually chronic. In the current case the horse showed an apparently acute onset with high fever and rapid clinical deterioration. A diagnosis of MEED should be considered in horses presenting with weight loss and skin lesions with or without fever. A final diagnosis is based on histological results of biopsy specimens from affected organs.     

Eosinophilic intestinal diseases of the horse

Eosinophilic intestinal diseases of the horse are not commonly reported. Similar diseases are reported in man, but for either species, these eosinophilic diseases, are poorly understood. Eosinophilic intestinal disease may be accompanied by eosinophilic disease of other organs, or eosinophilia may be restricted to the intestine. When infiltration of eosinophils is restricted to the intestine, horses have a good prognosis for resolution of clinical signs, even though the treatment may include celiotomy with intestinal decompression or resection and administration of a corticosteroid. When eosinophilic intestinal disease is accompanied by infiltration of other organs, such as skin, pancreas, lungs or liver, the horse's prognosis for survival is very poor.     

Clinical and histopathological features of pemphigus foliaceus with and without eosinophilic infiltrates: a retrospective evaluation of 40 dogs

The importance of cellular infiltrates in tissues has been investigated as a diagnostic tool, mechanism of pathogenesis, and prognostic indicator in certain human diseases. Eosinophils, in particular, have a distinct role in the development of cutaneous lesions in human autoimmune diseases. Identification of an eosinophilic infiltrate can aid the diagnosis of immunobullous disease in the early stages of the disease process. In canine pemphigus foliaceus, eosinophils are present to a variable degree within lesional tissue. This study retrospectively evaluated 40 dogs with pemphigus foliaceus, and examined clinical and histologic features and final outcomes in cases with and without eosinophilic infiltrates. Twenty‐five of 40 dogs (63%) had an eosinophilic infiltrate in either the pustules/crust, follicular infundibulum or dermis. There was no statistically significant difference in clinical distribution or appearance of dermatological lesions, response to treatment, or disease outcome in dogs with or without an eosinophilic infiltrate. However, dogs with concurrent disease were significantly more likely to have an eosinophilic infiltrate (P = 0.01). Dogs with adverse effects associated with immunosuppressive therapy were significantly more likely to have an eosinophilic infiltrate (P = 0.05). Fifteen of 40 dogs (38%) had a history of allergic disease and a significantly higher proportion of these dogs had an eosinophilic infiltrate (P = 0.04). An eosinophilic infiltrate was found in more than half of the dogs in this study. These findings justify further studies to investigate the role of eosinophils in the pathogenesis, therapy and prognosis in dogs with pemphigus foliaceus.     

Mucosal distribution of eosinophilic granulocytes within the gastrointestinal tract of horses

OBJECTIVES: To establish reference values for the range of the number of eosinophils found in equine gastrointestinal mucosa and to describe the distribution of this cell within the equine gastrointestinal mucosa. SAMPLE POPULATION: Gastrointestinal mucosal specimens from 14 adult horses euthanatized for reasons other than gastrointestinal disease. PROCEDURES: Gastrointestinal mucosal specimens were collected and grouped according to their anatomic regions. For histologic examination slides were stained with Luna's eosinophil stain to determine eosinophil accumulation and distribution. The mucosa was divided into 5 sections for each anatomic location, and the percentage of eosinophils in each of the 5 sections relative to the total eosinophil count in all sections was determined. Additionally, the number of eosinophils per square millimeter of mucosa was calculated as a measure of the degree of eosinophil accumulation. RESULTS: Lowest numbers of eosinophils were found in the stomach, and numbers increased from there to the cecum, then decreased from the ascending colon (right ventral colon, left ventral colon, pelvic flexure, left dorsal colon, and right dorsal colon) to small colon. In all gastrointestinal sections, most eosinophils were located near the muscularis mucosae and were rarely found near or on the luminal surface of the mucosa. CONCLUSIONS AND CLINICAL RELEVANCE: The distribution of eosinophils in the gastrointestinal tract of horses followed a pattern within the mucosa and between different sections of the gastrointestinal tract. The derived reference values and distribution data could be used to detect changes in eosinophil response in the equine gastrointestinal mucosa caused by diseases states.     

Cloning of equine chemokines eotaxin, monocyte chemoattractant protein (MCP)-1, MCP-2 and MCP-4, mRNA expression in tissues and induction by IL-4 in dermal fibroblasts

We report the cloning of four equine CC chemokines, eotaxin, monocyte chemoattractant protein (MCP)-1, MCP-2 and MCP-4, which show high levels of identity with their respective homologous sequences in other species. Using a multiplex RT-PCR, we have studied the constitutive mRNA expression of these four CC chemokines in skin, lung, liver, spleen, jejunum, colon and kidney of normal adult horses and compared this data with the eosinophil counts in the same samples. We demonstrate that eotaxin mRNA is only expressed in jejunum and colon, where there are large numbers of eosinophils suggesting that eotaxin might be recruiting eosinophils in the normal digestive tract of the horse. MCP-1 and MCP-4 are expressed in all tissues whereas MCP-2 is only found in some samples of lung, spleen, liver and kidney. We also report the early induction (2h) of equine eotaxin and MCP-4, and the up-regulation of MCP-1 by interleukin-4 in dermal fibroblasts, suggesting these chemokines might be involved in equine skin allergic diseases.     

Inflammatory bowel disease characterized by multisystemic eosinophilic epitheliotropic disease (MEED) in a horse in Saskatchewan,Canada

A 3-year-old Quarter Horse gelding was evaluated for chronic weight loss, diarrhea, and pruritus. Physical examination revealed several ulcerative lesions on the skin and mucosal membranes. Diagnostic imaging findings were consistent with enteritis, typhlitis, and colitis. Multisystemic eosinophilic epitheliotropic disease (MEED) was diagnosed upon necropsy. This disease may be considered a form of equine inflammatory bowel disease complex which can be challenging to diagnose, requiring histological assessment, and in some cases, the use of immunohistochemical markers.Key clinical message:Multisystemic eosinophilic epitheliotropic disease is challenging to diagnose but should be considered in horses with chronic weight loss that fail to respond to conventional treatment for concurrent diarrhea and skin lesions.     

Multisystemic eosinophilic epitheliotropic disease (MEED) in a horse

Extract

A 6-year-old Thoroughbred-cross gelding was presented with ulcerative coronitis and sloughing of chestnuts and ergots. The horse was mildly lame and its faeces were soft and formless. Laboratory findings included a mild eosinophilia, mild hyperglobuli-naemia and a marked elevation of gamma glutamyl transferase and glutamate dehydrogenase. There was a general deterioration of the horse's condition over a 3-week period and the dermatitis became generalised and the diarrhoea severe. It was euthanised. At necropsy, the pancreas was pale, multinodular and firm. The liver had a lobular appearance and there was generalised thickening of the descending colon. Histologically, there was a marked, predominantly eosinophilic infiltrate of the pancreas, liver and colon. There was a superficial and deep perivascular dermatitis of the coronet, characterised by dense infiltrates of eosinophils in association with marked acanthosis and hyperkeratosis. The combination of clinical findings, haematology, serum biochemistry and gross changes in conjunction with the histology confirmed MEED. The aetiology of MEED has not been established.     

Eosinophilic crystalline pneumonia as a major cause of death in 129S4/SvJae mice

Eosinophilic crystalline pneumonia is an idiopathic disease that occurs in many strains and stocks of mice, more commonly in strains on a C57BL/6 background. The disease occurs sporadically in most strains of mice and varies from mild and subclinical to severe and fulminating, sometimes resulting in respiratory distress and death. In this study, 94 aged male and female 129S4/SvJae mice were evaluated for eosinophilic crystalline pneumonia lesions. There was an 87% incidence, with females overrepresented. Histologically, there were multifocal to coalescing inflammatory infiltrates composed of numerous large eosinophilic macrophages and multinucleate cells admixed with eosinophils, neutrophils, lymphocytes, and plasma cells within alveolar and bronchiolar spaces, associated with refractile, brightly eosinophilic, angular crystals. Alveolar macrophages and multinucleate cells contained fine needlelike to rectangular intracytoplasmic crystalline material. Similar crystals were often free within alveoli and conducting airways, often associated with mucous metaplasia of bronchiolar epithelium. This disease may occur spontaneously or in concert with other pulmonary lesions, such as pulmonary adenomas, lymphoproliferative disease, allergic pulmonary disease, and parasitic or fungal infections. The characteristic crystals morphologically resemble Charcot-Leyden crystals, which represent eosinophil breakdown products in humans with eosinophil-related disease. However, crystals in eosinophilic crystalline pneumonia are composed predominantly of Ym1 protein, a chitinase-like protein associated with neutrophil granule products and secreted by activated macrophages. The function of Ym1 protein is not fully understood but is believed to be involved in host immune defense, eosinophil recruitment, and cell-cell and cell-matrix interactions consistent with tissue repair. The mechanism of induction of eosinophilic crystalline pneumonia with Ym1 crystal formation is unknown.     

Daily variability of equine fecal strongyle egg counts.

Fecal egg counts often are used for diagnosing equine strongyle infections and estimating the number of eggs shed in the feces. An individual egg count should be interpreted in view of the normal fluctuation of egg numbers in an individual horse. In this study, the daily variability of strongyle fecal egg counts from horses was investigated. The Cornell-McMaster egg-counting technique was used to estimate the eggs per gram of feces in repeated daily fecal samples from 39 horses. The variation of the daily egg counts across 4 days was greater than would be expected if a consistent number of eggs were produced and dispersed randomly in the feces. The means and variances of the daily counts from each horse had a logarithmic relationship. For practical purposes, however, the fluctuation of egg counts is low enough for the fecal egg count to be used to identify horses for treatment, to estimate pasture contamination, or to assess response to therapy.     

Eosinophilic myeloproliferative disorder in a horse

An eosinophilic myeloproliferative disorder resulted in edema and hemorrhagic diathesis in a 10-month-old Standardbred colt. Laboratory abnormalities included severe thrombocytopenia, anemia, mild hypoproteinemia, and marked eosinophilia. Circulating eosinophils were immature or atypical with variation in granule size, disproportionate nuclear to cytoplasmic maturation, and abnormal nuclear size and shape. Bone marrow aspirate had mainly atypical eosinophil precursors, few erythroid precursors, and no megakaryocytes. A blood transfusion and dexamethasone therapy resulted in some improvement; however, the horse was euthanatized due to poor prognosis. Postmortem examination showed gastrointestinal parasitism; histologically the spleen was infiltrated by atypical eosinophils and there were sites of eosinophilopoiesis. The disease was broadly similar to idiopathic hypereosinophilic syndrome in people, but typical cardiac and neurologic involvement of hypereosinophilic syndrome were absent. Progressive myelophthesis and marked eosinophil atypia suggested malignancy.     

Eosinophils: A review

The eosinophil was discovered by Jones in 1846 (Dessein and David, 1982) but its proclivity to stain with aniline dyes was first described by Paul Ehrlich in 1879 (Hirsch and Hirsch, 1980). Recognized and named for this quality, eosinophils possess an abundance of highly basic proteins within their granules which confer their affinity for acidic dyes (Gleich and Loegering, 1984).Eosinophils are traditionally viewed as killer-effector cells in parasitic infestations and as modulators of Type I hypersensitivity reactions (Butterworth and David, 1981; Kay, 1985). The eosinophils' reserve of cationic proteins and enzymes which imparts their profound parasiticidal effects (Butterworth and David, 1981) contrasts with this leukocyte's purported regulatory function in inflammation (Kay, 1985; Fechteret al., 1986). The opposing functions possessed by this leukocyte exemplify the enigma of the eosinophil. Recent evidence suggests that although the eosinophil does possess some regulatory capabilities, its presence is, in fact, a harbinger of tissue destruction (Gleich and Adolphoson, 1986, Wardlaw and Kay, 1987; Spry, 1988). Nor does the presence of the eosinophil automatically infer IgE mediated hypersensitivity, as evidenced by studies examining the interaction of the eosinophil with the cellular arm of the immune system (Basten and Beeson, 1970; Ruscettiet al., 1976; Beeson and Bass, 1977; Raghavacharet al., 1987; Ohnishiet al., 1988).The purpose of this review is to provide a brief overview of the structure and biology of the mammalian eosinophil and to emphasize the fact that eosinophils fulfil a paradoxical role as effectors of tissue damage and as benign modulators of inflammation.     

Borrelia burgdorferi infections with special reference to horses. A review

Summary This review discusses the literature on B. burgdorferi infections in view of the rising incidence of this infection in general and the increasing concerns of horse owners and equine practitioners. Lyme disease, the clinical expression of Borrelia infections in man is an important health problem. The geographic distribution of B. burgdorferi infections in equidae should resemble that of human cases because the vector tick involved, Ixodes ricinus, feeds on both species and, indeed, the infection has been established many times in horses. However, a definite diagnosis of the disease "Lyme borreliosis" in human beings as well as in horses and other animals is often difficult to accomplish. Although a broad spectrum of clinical signs has been attributed to B. burgdorferi infections in horses, indisputable cases of equine Lyme borreliosis are extremely rare so far, if they exist at all.     

Borrelia burgdorferi infections with special reference to horses. A review

This review discusses the literature on B. burgdorferi infections in view of the rising incidence of this infection in general and the increasing concerns of horse owners and equine practitioners. Lyme disease, the clinical expression of Borrelia infections in man is an important health problem. The geographic distribution of B. burgdorferi infections in equidae should resemble that of human cases because the vector tick involved, Ixodes ricinus, feeds on both species and, indeed, the infection has been established many times in horses. However, a definite diagnosis of the disease "Lyme borreliosis" in human beings as well as in horses and other animals is often difficult to accomplish. Although a broad spectrum of clinical signs has been attributed to B. burgdorferi infections in horses, indisputable cases of equine Lyme borreliosis are extremely rare so far, if they exist at all.     

The Domestic Livestock Resources of Turkey: Occurrence and Control of Diseases of Horses,Donkeys and Mules

Horses, donkeys, and mules have been important in Turkey for agriculture, transport, and the military for hundreds of years. Equids number more than 0.5 million in Turkey. Most horses are local types but emphasis is now on Thoroughbreds and Arabians for racing and competitions. New roles have not materialized for donkeys and mules that continue to perform their traditional activities. Disease control is assured mainly by public services acting within laws governing diseases and welfare. African horse sickness, glanders, dourine, equine infectious anemia, vesicular stomatitis, equine encephalomyelitis, anthrax, and rabies are notifiable diseases but none of the mainly equine diseases has been reported in Turkey for many years. Several zoonoses, including toxoplasmosis, brucellosis, listeriosis, and Rhodococcus infections, have been identified by serodiagnosis over wide areas, but animals carrying antibodies rarely exhibit clinical symptoms. Among other diseases in Turkish Equidae are piroplasmosis, respiratory infections, contagious equine metritis and equine influenza. Other viral and bacterial pathogens have been identified in isolated investigations. Internal and external parasites are a major cause of economic loss. Much research on equine diseases has been undertaken in the last decade of the 20th and first decade of the 21st centuries, perhaps because of Turkey's possible accession to the European Union and the goal to harmonize identification and control procedures and also because of the country's increasing participation in international equine events. This paper reviews animal health services and provides a bibliography of more than 100 references covering horse, donkey, and mule diseases in Turkey.     

Pulmonary and hepatic eosinophilic granulomas and epistaxis in a horse suggestive of multi‐systemic eosinophilic epitheliotropic disease

Multi‐systemic eosinophilic epitheliotropic disease (MEED) is a relatively uncommon disease characterised by eosinophilic infiltration of more than one organ system, with the skin and gastrointestinal tract most commonly affected. This case report describes a gelding that presented for weight loss, increased respiratory rate and effort and chronic intermittent epistaxis. During post mortem examination diffuse eosinophilic granulomatous lesions were identified in the lung and liver, leading to a diagnosis of MEED. Veno‐occlusive pulmonary remodelling was also discovered, believed to be the cause of the chronic epistaxis and a result of the pulmonary fibrosis and eosinophilic granulomas.